Which IPv4 private address class should I use ?

Private IP addresses are defined in RFC 1918. Theses addresses can be used on a private network, but they’re not routable through the Internet. By using private IP addresses, ISPs, corporations and home users can use some times only one public IP address to connect all internal systems to the internet. This is very economical because private IP addresses can be used on inside and the technologies like NAT (Network Address Translation) can be used to communicate with outside world.

 

Reserved Address Space

Class A 10.0.0.0 through 10.255.255.255

Class B 172.16.0.0 through 172.31.255.255

Class C 192.168.0.0 through 192.168.255.255

RFC 1918

 

  • Private addresses are not globally routable on the Internet
  • 1 Network in Class A, 16 Networks in Class B, 256 Networks in Class C
  • RFC 1918 was created to establish a range of IP addresses that are dedicated to use on internal networks.
  • RFC 1918 was created to delay the transition to IPv6
  • The private address must be filtered at Internet border interfaces
  • NAT is required on Internet border device

 

Many IT departments straggle with simple question: Which private address class should I use A, B or C.

 

The rule of thumb in the consulting world is to use Class A network address for any corporate type of network unless there is special circumstances. This gives you the most flexibility and growth options.

For example, if you used the 10.0.0.0 network address with a /24 mask, then you’d have 65.536 networks, each with 254 hosts. This gives you enough addresses for almost any network.

For home Network you can use Class C address because it is the easiest to understand. It will give you 254 hosts which is plenty for home network.